Testing transformer impact closing excitation inrush current suppression device and method

Abstract

The invention discloses a test transformer impact closing excitation inrush current suppression device and a test transformer impact closing excitation inrush current suppression method. The device comprises a transformer closing circuit breaker connected with a test transformer and a maintenance power box, soft starters connected in parallel, a current-limiting resistor connected in series and an isolation contactor which are uniformly regulated and controlled by a control unit. The input end of the transformer is provided with a detection module for monitoring current and voltage parameters, and the capacity of the soft starter is 5%-10% of that of the transformer. An inrush current suppression algorithm is built in the control unit, the initial voltage, the voltage rise curve and the current limiting time of the soft starter are calculated according to the transformer capacity and the rated current, and the inrush current is accurately suppressed through hierarchical calculation and dynamic adjustment. Besides, the device also has the functions of adjustable current-limiting resistance, historical data correction algorithm, remote data transmission and the like, can realize accurate dynamic current limiting, control strategy optimization and remote monitoring, effectively reduces the impact of excitation inrush current on the transformer and the system, and improves the operation safety and reliability of the test transformer.

Description

Technical Field

[0001] This invention relates to the field of power system equipment technology, and in particular to a device and method for suppressing inrush current during the impulse closing of a test transformer. Background Technology

[0002] During generator maintenance, test transformers are typically used as temporary mobile equipment connected to the maintenance power system. Currently, the power supply for test transformers is generally drawn from maintenance power boxes located near the maintenance site, with a capacity typically ranging from 100 to 250A. However, at the moment the test transformer is switched on, a large inrush current is generated due to factors such as core saturation. This current can reach 15-20 times the rated current, easily triggering malfunctions in upstream protection devices and causing cascading trips. Hydropower plants often employ complex power transmission procedures to ensure safe power supply, which further severely impacts the testing progress, increasing maintenance time and costs. Summary of the Invention

[0003] The purpose of this invention is to provide a device and method for preventing inrush current during the impulse closing of a test transformer. By using current-limiting magnetization technology, the inrush current during closing is effectively suppressed, avoiding cascading tripping, simplifying the power supply process, and improving test efficiency.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a test transformer impulse closing excitation inrush current suppression device, including a transformer closing circuit breaker connecting the test transformer and the maintenance power supply box, a soft starter connected in parallel with the transformer closing circuit breaker, a current limiting resistor and an isolation contactor connected in series with the soft starter, and a control unit that controls the soft starter, the isolation contactor and the transformer closing circuit breaker. The control unit is configured with the initial voltage, voltage rise curve and current limiting time of the soft starter according to the transformer capacity and rated current.

[0005] Preferably, the input terminal of the transformer is connected to a detection module, which includes a current sensor and a voltage sensor for monitoring the input parameters of the transformer.

[0006] Preferably, the detection module is connected to the control unit.

[0007] Preferably, the capacity of the soft starter is 5%-10% of the transformer capacity.

[0008] Preferably, the current-limiting resistor is an adjustable resistor, and the control unit controls the resistance value of the current-limiting resistor to be adjusted within the range of 0 to the maximum resistance value according to the calculation result of the inrush current suppression algorithm.

[0009] Preferably, the control unit is also connected to a storage module, which stores historical closing data of different types of test transformers. The inrush current suppression algorithm corrects the currently calculated soft starter output voltage curve and current limiting time based on the historical closing data.

[0010] Preferably, the control unit integrates a communication module, which is used to upload the transformer input parameters, soft starter operating status and inrush current suppression process data monitored by the detection module to the remote monitoring terminal.

[0011] Preferably, the control unit is equipped with an inrush current suppression algorithm, which can automatically calculate the output voltage curve and current limiting time of the soft starter based on the capacity and rated current of the transformer; The inrush suppression algorithm includes the following steps: Step 1: Obtain the transformer capacity (Unit: kVA), Rated Current (Unit: A), and the voltage at the moment the transformer is switched on is collected in real time through the detection module. Current ; Step 2: Based on the transformer capacity With rated current Calculate the initial current limiting current The calculation formula is: ,in This is the current limiting coefficient, and its value range is... ; Step 3: Based on the initial voltage ( , This is the rated voltage of the transformer. Value and voltage rise slope Generate the initial voltage rise curve ; Among them, voltage rise slope The calculation formula is: , This is the voltage-capacity regulation coefficient, with a value range of [value missing]. , This is the capacity compensation coefficient, and its value range is... , Transformer capacity (unit: kVA); Step 4: During the closing process, the detection module provides real-time current feedback. With voltage ,like The control unit immediately triggers the isolation contactor to operate, increases the current-limiting resistor input, and simultaneously adjusts the voltage rise curve to... , according to Linear adjustment of the difference; Step 5: When continuous Second( The value is set according to the transformer capacity. (seconds) stabilized at ( When the voltage is within the specified range, the control unit controls the soft starter to output voltage to the rated voltage, thus completing the inrush current suppression process.

[0012] A method for suppressing inrush current during the closing of a test transformer, using the aforementioned suppression device, includes the following steps: Step 1: Preparation stage, install and connect the soft starter, current limiting resistor, isolation contactor and control module; Step 2: Based on the capacity and rated current of the test transformer, set the initial voltage, voltage rise slope, and current limiting time of the soft starter in the control module; Step 3: When closing the transformer under test, the control module issues a closing command. The control module first controls the isolation contactor to close, starts the soft starter, and supplies power to the transformer through the current-limiting resistor box to start the magnetization process. Step 4: The soft starter gradually increases the output voltage according to the preset voltage curve until it reaches the rated voltage. After the output voltage of the soft starter stabilizes, the control module closes the transformer closing circuit breaker, directly connecting the transformer to the power supply. Then, the isolation contactor is disconnected and the soft starter stops working, completing the closing process.

[0013] Preferably, during the energization of the transformer, when the detection unit detects that the input current of the transformer exceeds a safety threshold, the detection unit transmits a signal to the control module, and the control module automatically adjusts the soft starter parameters or interrupts the operation.

[0014] This invention provides a device and method for suppressing inrush current during the impulse closing of a test transformer, which has the following beneficial effects.

[0015] 1. By combining a soft starter and a current-limiting resistor, the inrush current can be reduced from 15-20 times the rated current of the traditional closing method to 8-15A, effectively avoiding the problem of over-tripping caused by excessive inrush current.

[0016] 2. Since the inrush current is effectively controlled, the hydropower plant no longer needs to perform a complex power transmission process and can directly perform the closing operation, which greatly improves the testing efficiency and shortens the maintenance time.

[0017] 3. The PLC or microcontroller control system is used to achieve automated operation. Combined with a real-time monitoring and feedback mechanism, it ensures that the device can operate reliably under various working conditions, thereby improving the stability and safety of the system.

[0018] 4. The soft starter is designed with a capacity of 5%-10% of the transformer capacity, making it suitable for test transformers of different capacities and providing good versatility and expandability. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a connection diagram according to an embodiment of the present invention.

[0020] Figure 2 This is a circuit diagram of an embodiment of the present invention. Detailed Implementation

[0021] like Figure 1 and Figure 2 As shown, the present invention provides a test transformer impulse closing excitation inrush current suppression device, including a transformer closing circuit breaker connecting the test transformer and the maintenance power supply box, a soft starter connected in parallel with the transformer closing circuit breaker, a current limiting resistor and an isolation contactor connected in series with the soft starter, and a control unit that controls the soft starter, the isolation contactor and the transformer closing circuit breaker. The control unit is configured with the initial voltage, voltage rise curve and current limiting time of the soft starter according to the transformer capacity and rated current.

[0022] Taking a 500kVA test transformer as an example, the power supply box output voltage is 380V. In the device, the transformer closing circuit breaker is a model with a rated current of 630A, connected in parallel with a soft starter with a rated capacity of 50kVA. The soft starter is connected in series with a fixed current-limiting resistor of 10Ω and an isolating contactor with a rated current of 400A. The control unit uses a PLC controller, which is built-in based on the transformer capacity of 500kVA and the rated current of 722A (determined by...). calculate, The preset initial voltage of the soft starter (0.3 times the rated voltage of 400V, i.e., 120V), voltage rise curve, and current limiting time (set to 8 seconds) are configured. During actual operation, the control unit controls the components to work together according to the preset parameters to achieve inrush current suppression.

[0023] Based on Example 1, a detection module is installed at the input end of the test transformer. A Hall effect current sensor with a range of 0-1000A and an accuracy of 0.5 is selected, and a resistance voltage divider type voltage sensor with a range of 0-500V and an accuracy of 0.2 is used. During transformer closing, the current sensor monitors the input current in real time, and the voltage sensor monitors the input voltage. Both sensors transmit the collected parameter signals to the control unit, providing data support for inrush current suppression.

[0024] The current and voltage sensors of the detection module are connected to the analog input module of the control unit via a 4-20mA analog signal line. The control unit performs A / D conversion and filtering on the collected current and voltage signals to accurately determine the transformer's operating status and adjust the operating parameters of components such as the soft starter in a timely manner.

[0025] For a test transformer with a capacity of 800kVA, a soft starter with a capacity of 80kVA (10% of 800kVA) was selected. In the transformer's impulse closing test, the soft starter's capacity was appropriate, which could effectively suppress the inrush current, avoid cost waste and resource idleness caused by excessive capacity, and meet the power requirements of the transformer during startup.

[0026] Taking a 1000kVA test transformer as an example, the operation process of the inrush current suppression algorithm is explained. The transformer capacity is obtained. Rated current Voltage at the moment of closing Current Calculate the initial current-limiting current. Initial voltage ; The value is 0.3; voltage rise slope Generate the initial voltage rise curve If during the closing process, if... The control unit triggers the isolation contactor to operate, increasing the current-limiting resistor input and adjusting the voltage rise curve until... Stable for 4 consecutive seconds Within this range, the output voltage of the soft starter is controlled to reach the rated voltage.

[0027] While limiting the initial voltage is necessary to suppress inrush current, the voltage cannot be too low either. Otherwise, the transformer may fail to start normally, or the core may not be effectively magnetized due to insufficient voltage during startup, resulting in abnormal vibration and noise, which will affect the service life of the equipment. Extensive testing and practical engineering verification have shown that 0.2–0.4 times the rated voltage can both avoid inrush current problems caused by excessively high voltage and provide sufficient energy for the transformer core to smoothly enter normal operating conditions, ensuring a stable transformer startup.

[0028] During the preparation phase, install the soft starter (10kVA capacity), 15Ω current-limiting resistor, isolating contactor, and control module. In the control module, based on the transformer capacity and rated current, set the initial voltage to 80V, the voltage rise slope to 0.02, and the current-limiting time to 6 seconds. During closing, the control module first closes the isolating contactor, starts the soft starter, and supplies power through the current-limiting resistor. After the soft starter raises the voltage to the rated voltage according to the preset curve, the control module closes the transformer closing circuit breaker, then opens the isolating contactor and stops the soft starter, completing the closing process.

[0029] When the transformer is energized, if the current sensor in the detection unit detects that the input current reaches 150A (exceeding the safety threshold of 120A), it immediately transmits a signal to the control module. After receiving the signal, the control module automatically reduces the rise rate of the soft starter's output voltage and extends the current limiting time. If the current still exceeds the threshold, the operation is interrupted, the transformer power supply is cut off, and the equipment safety is ensured.

[0030] Taking a 300kVA test transformer as an example, an adjustable resistor with a resistance range of 0-20Ω is selected. Based on the inrush current suppression algorithm, the control unit adjusts the current-limiting resistor value to 12Ω at the moment the transformer is closed. As the closing process progresses, if the current is detected to be lower than the threshold, the control unit gradually reduces the resistance value until the current stabilizes, thus achieving dynamic current limiting.

[0031] The control unit is connected to a storage module, which stores historical closing data for 10 different types of test transformers. When closing a new 400kVA transformer, the inrush current suppression algorithm first calculates initial parameters based on the transformer's capacity and rated current, then retrieves closing data of transformers with similar capacities from historical data to correct the calculated soft starter output voltage curve and current limiting time, thereby optimizing the inrush current suppression effect.

[0032] The control unit integrates a 4G communication module. During the operation of the test transformer, the communication module uploads real-time current and voltage data monitored by the detection module, the operating status of the soft starter (such as output voltage, current, and operating mode), and key data in the inrush current suppression process (such as the number of times the current limiting resistor is adjusted and voltage adjustment records) to the remote monitoring terminal, facilitating remote monitoring and fault diagnosis by technicians.

Claims

1. A device for suppressing inrush current during the closing of a test transformer, characterized in that: It includes a transformer closing circuit breaker that connects the test transformer and the maintenance power supply box. The transformer closing circuit breaker is connected in parallel with a soft starter. The soft starter is connected in series with a current-limiting resistor and an isolation contactor. It also includes a control unit that controls the soft starter, the isolation contactor and the transformer closing circuit breaker. The control unit is configured with the initial voltage, voltage rise curve and current-limiting time of the soft starter according to the transformer capacity and rated current.

2. The inrush current suppression device for test transformer impulse closing excitation as described in claim 1, characterized in that: The control unit is equipped with an inrush current suppression algorithm, which can automatically calculate the output voltage curve and current limiting time of the soft starter based on the transformer's capacity and rated current. The inrush suppression algorithm includes the following steps: Step 1: Obtain the transformer capacity Rated current The voltage at the moment the transformer is switched on is collected in real time through the detection module. Current ; Step 2: Based on the transformer capacity With rated current Calculate the initial current limiting current The calculation formula is: ,in This is the current limiting coefficient; Step 3: Based on the initial voltage , , The rated voltage of the transformer, and the voltage rise slope. Generate the initial voltage rise curve ; Among them, voltage rise slope The calculation formula is: , This is the voltage-capacity regulation coefficient, with a value range of [value missing]. , This is the capacity compensation coefficient. For transformer capacity; Step 4: During the closing process, the detection module provides real-time current feedback. With voltage ,like The control unit immediately triggers the isolation contactor to operate, increases the current-limiting resistor input, and simultaneously adjusts the voltage rise curve to... , according to Linear adjustment of the difference; Step 5: When continuous Stabilizes in seconds When the voltage is within the specified range, the control unit controls the soft starter to output voltage up to the rated voltage. This completes the inrush current suppression process.

3. The inrush current suppression device for test transformer impulse closing excitation as described in claim 1, characterized in that: The transformer input terminal is connected to a detection module, which includes a current sensor and a voltage sensor, for monitoring the transformer input parameters.

4. The inrush current suppression device for test transformer impulse closing excitation as described in claim 3, characterized in that: The detection module signal is connected to the control unit.

5. The inrush current suppression device for test transformer impulse closing excitation as described in claim 1, characterized in that: The capacity of the soft starter is 5%-10% of the transformer capacity.

6. The inrush current suppression device for test transformer impulse closing excitation as described in claim 2, characterized in that: The current-limiting resistor is an adjustable resistor, and the control unit controls the resistance value of the current-limiting resistor to be adjusted within the range of 0 to the maximum resistance value based on the calculation results of the inrush current suppression algorithm.

7. The inrush current suppression device for test transformers as described in claim 1, characterized in that: The control unit is also connected to a storage module, which stores historical closing data of different types of test transformers. The inrush current suppression algorithm corrects the currently calculated soft starter output voltage curve and current limiting time based on the historical closing data.

8. The inrush current suppression device for test transformer impulse closing excitation as described in claim 1, characterized in that: The control unit integrates a communication module, which is used to upload the transformer input parameters, soft starter operating status and inrush current suppression process data monitored by the detection module to the remote monitoring terminal.

9. The method for suppressing inrush current during impulse closing of a test transformer as described in claim 8, characterized in that, The application of the above-mentioned suppression device includes the following steps: Step 1: Preparation stage, install and connect the soft starter, current limiting resistor, isolation contactor and control module; Step 2: Based on the capacity and rated current of the test transformer, set the initial voltage, voltage rise slope, and current limiting time of the soft starter in the control module; Step 3: When closing the transformer under test, the control module issues a closing command. The control module first controls the isolation contactor to close, starts the soft starter, and supplies power to the transformer through the current-limiting resistor box to start the magnetization process. Step 4: The soft starter gradually increases the output voltage according to the preset voltage curve until it reaches the rated voltage. After the output voltage of the soft starter stabilizes, the control module closes the transformer closing circuit breaker, directly connecting the transformer to the power supply. Then, the isolation contactor is disconnected and the soft starter stops working, completing the closing process.

10. The method for suppressing inrush current during impulse closing of a test transformer as described in claim 9, characterized in that: During the energization of the transformer, when the detection unit detects that the input current of the transformer exceeds the safety threshold, the detection unit transmits a signal to the control module, and the control module automatically adjusts the soft starter parameters or interrupts the operation.

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